1. Technical Field
This invention relates generally to optical filters and associated systems, and more particularly to a variable reflectance notch filter and laser-based image projection systems employing the same.
2. Background Art
Laser projection devices facilitate the production of brilliant images created with vibrant colors. Laser projection systems are generally brighter, sharper, and have a larger depth of focus than do conventional projection systems. Further, the advent of semiconductor lasers and laser diodes allows laser projection systems to be designed as compact projection systems that can be manufactured at a reasonable cost. These systems consume small amounts of power yet deliver bright, complex images.
For the reasons set forth above, lasers are frequently used in sophisticated projection systems such as head-up displays. In a head-up display, lasers present information to a user along a projection surface that is semi-transparent. The user may accordingly see the information without having to move their eyes from their primary viewing position to read the information. Once only available in expensive systems such as military aircraft, head-up systems are now becoming commercially available to consumers as well.
One issue making the incorporation of laser projection systems into some applications is temperature. Illustrating by way of example, it would be desirable to incorporate a head-up system into a vehicle so that the user may see information without having to divert their eyes from the road. However, in automotive applications the temperature within an automobile can vary by more than one hundred degrees Celsius. While prior art systems provide adequate performance within a narrow temperature range, performance can be compromised at temperature extremes due to the changes in emitted wavelength across temperature.
There is thus a need for an improved projection system offering improved performance across large temperature ranges.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.